Transcutaneous telemetry of cerebrospinal fluid shunt programmable-valve pressure using near-infrared (nir) light

ABSTRACT

An improvement for a programmable valve system of the type implanted in a patient and used to divert cerebrospinal fluid (CSF) from an intraventricular space to a terminus such as the peritoneal cavity. Such system includes means for establishing a flow path for the CSF to the terminus, which flow path includes a normally closed valve and means for adjusting the opening pressure of the valve in order to regulate the quantity of CSF diverted. The improvement enables an operator to be apprised of the actual opening pressure setting of the valve. A sensor is implantable at the patient and responds to the actual opening pressure setting, by generating an NIR telemetry signal indicative of the actual setting. This signal is transcutaneously transmitted through the skin of the patient to an external point. The telemetry signal is processed to produce observer intelligible data indicating the opening pressure setting of the valve.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation-In-Part claiming priority benefitfrom U.S. patent application Ser. No. 11/067,497 entitled“Transcutaneous Telemetry Of Cerebrospinal Fluid ShuntProgrammable-Valve Pressure Using Near-Infrared Light” filed on Feb. 25,2005 which claims priority from U.S. Provisional Applications 60/547,691filed Feb. 25, 2004; 60/577,807 filed Jun. 8, 2004; and 60/582,337 filedJun. 23, 2004.

FIELD OF INVENTION

This invention relates generally to transcutaneous telemetry with animplantable biomedical device, and more specifically relates to a systemwhich allows transcutaneous telemetry of a programmed valve openingpressure via near-infrared (NIR) light.

BACKGROUND OF THE INVENTION

Fluidic shunts are commonly employed for the diversion of cerebrospinalfluid from the cranial intraventricular space to a terminus such as theperitoneal cavity in the treatment of hydrocephalus. The quantity ofcerebrospinal fluid (CSF) diverted by the shunt may be altered byadjusting the opening pressure of a normally closed integral valve.Several valve designs (e.g. Codman-Hakim® valve, Medtronic Strata®valve) allow transcutaneous adjustment, or programmability, of theopening pressure via a transcutaneously applied magnetic field.

The programmed valve pressure is dependent upon the position of theexternal programmer relative to the implanted valve. Because the valveis implanted beneath the skin, the exact orientation of the valve is notalways apparent. Malpositioning of the programmer can introduce errorsinto the programming process and result in erroneous pressures beingprogrammed. Therefore, it is desirable to be able to confirm the actualprogrammed pressure after reprogramming or as clinical conditionswarrant. By “actual” programmed pressure is meant the de facto pressurewhich has been set for opening of the valve as opposed to the pressurewhich may be assumed to have been set as a result of the operator'smanual adjustment.

While the Medtronic Strata® valve provides a transcutaneous means ofmagnetically indicating the valve pressure setting, the Codman-Hakimvalve requires the use of an x-ray to determine the valve setting. Theuse of x-ray to determine valve pressure is undesirable as it is costly,time-consuming, and exposes the patient to ionizing radiation.

SUMMARY OF INVENTION

The invention disclosed herein provides an improvement pertinent toexisting programmable valve systems which allows transcutaneoustelemetry of programmed valve opening pressure via near-infrared (NIR)light. NIR light easily penetrates body tissues such as the scalp, andthe light beam may be modulated to encode data for transcutaneoustransmission. The actual valve pressure setting is determined by anattached cam. An optical disc coaxially mounted with the cam opticallyencodes the valve position and these data are transmittedextracorporally via NIR light.

Light in the near-infrared spectrum is easily transmitted through theskin and is detected by an external sensor head and associatedelectronics. Indefinite longevity and small size is attained in theimplant by not incorporating a power source within the module. Instead,power is derived inductively through rectification of atranscutaneously-applied high-frequency alternating electromagneticfield which is generated by a power source within the external couplingmodule, in concept much like a conventional electrical transformer. Theextracorporeal components of the system calculate the actual valveopening pressure setting.

The present invention overcomes the aforementioned disadvantages ofexisting technologies by providing a means for telemetric conveyance ofphysiological data via transcutaneous projection of a near infraredlight beam. The use of this technique for telemetry of intracranialpressure and other applications is set forth in U.S. Pat. No. 7,435,229to Wolf filed Feb. 24, 2005. The entire disclosure of that applicationis hereby incorporated herein by reference.

The NIR spectrum is defined as 750-2500 nm. Choice of the preferred NIRwavelength for transcutaneous telemetry pursuant to the presentinvention is dependent upon the absorption coefficients of theintervening tissues. The absorption by melanosomes dominates over thevisible and near-infrared spectra to about 1100 nm, above which freewater begins to dominate. Absorption by the dermis decreasedmonotonically over the 700-1000 nm range. Whole blood has a minimumabsorption at about 700 nm but remains low over the 700-1000 nm range.The nadir in the composite absorption spectrum therefore lies in the800-1000 nm range.

The actual wavelength utilized is therefore dictated by-the optimalspectral range (as above) and the availability of suitable semiconductoremitters. Several suitable wavelengths may include, but are not limitedto: 760 nm, 765 nm, 780 nm, 785 nm, 790 nm, 800 nm, 805 nm, 808 nm, 810nm, 820 nm, 830 nm, 840 nm, 850 nm, 870 nm, 880 nm, 900 nm, 904 nm, 905nm, 915 nm, 920 nm, 940 nm, 950 nm, 970 nm, and 980 nm. Wavelengthsoutside this range may be used but will be subject to greaterattenuation by the intervening tissues.

BRIEF DESCRIPTION OF DRAWINGS

The invention is diagrammatically illustrated, by way of Example, in thedrawings appended hereto, in which:

FIG. 1 is a simplified longitudinal cross sectional diagram illustratinghow the sensor may be implanted in a typical use with a patient;

FIG. 2 is a schematic diagram, partially in block form, illustrating anoverall system in accordance with the invention;

FIG. 3 is an electrical schematic diagram of the valve pressuretransducer and associated components; and

FIG. 4 is a schematic block diagram of the valve position sensorcomponents which are external to the patient.

FIG. 5 is a non-schematic diagram of the relationship and positioning ofthe optical encoder and magnetic flux coupling of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The system of the present invention as shown in the simplifiedcrosssectional view of FIG. 1 includes an extracorporeal sensor head 70which provides an interface to a human operator and which telemeterswith an implanted component 14. The latter is integrated into theshunt-valve housing, detects the actual valve setting, and telemetersthese data to the extracorporeal sensor head 70. The implanted component14 may derive its power via inductive coupling from the extracorporealsensor head 70.

In a typical in vivo implementation a hollow ventricular catheter 3 isplaced surgically into a cerebrospinal fluid (CSF) filled ventricle 2 ofthe brain 6 of the patient. The CSF is communicated via the ventricularcatheter 3 to the implanted component 14 where its flow is controlled bycontrollable pressure valve 18 (FIG. 2). The normally closed valveopening pressure setting is controlled by an attached cam which ismounted on a rotatable axis. An optical disc on that axis acts withother elements to encode the valve position, data for which istransmitted extracorporally through skin 20 via NIR light to sensor head70. Depending on valve position, the CSF may exit the implanted sensor14 and passes, via distal catheter 4, ultimately to the peritonealcavity of the abdomen (not shown) or other appropriate point. Theimplanted sensor 14 is installed superficial to, or embedded within theskull 5.

FIG. 2 depicts a schematic block diagram of a preferred embodiment ofthe ICP Valve transducer system. FIG. 5 shows a non-schematic diagram ofthe relationship and positioning of the optical encoder disk andmagnetic flux coupling. External programmer 16 is an extracorporealdevice which is used to set the opening pressure of a programmablepressure valve 18 which is implanted beneath the skin (scalp) 20 of thepatient. The opening pressure of normally closed valve 18 dictates themaximum pressure gradient between the cerebrospinal fluid compartmentwhich is connected to inlet 22 to valve 18, and the outflow for which isvia outlet 24. The valve 18 pressure setting is dependent upon theposition of a cam which rotates around the valve's mechanical axis 26.

The external programmer 16 is able to modify the rotational position ofthe valve 18 and mechanical axis 26 via magnetic flux coupling 28between an external magnet 30 and a magnet 32 fixedly attached to themechanical axis 26 of the valve mechanism. The technology referenced byitems 16 through 32 is described in the prior art.

In prior art valves exemplified by valve 18, detents within the valvemechanism define specific rotational angles in which the valve mechanismaxis 26 may remain in a static position. In the preferred embodiment ofthe current invention, an optical encoder disc 34 secured to axis 26 isan optically opaque disc with radially oriented perforations (oroptically transparent windows) which encode binary numerals. Eachspecific static rotational angle which may be assumed by the valvemechanism axis 26 has a corresponding unique encoded binary numeral, n.An NIR light beam 36 transilluminates the optical encoder disc 34 suchthat the binary encoded numeral, n, may be detected by photodetectorarray 38. In the preferred embodiment, these encoded numerals arearranged sequentially around the disc 34 ranging from 1 to ‘N’ where Nis the total number of discrete static positions of the valve mechanismaxis 26. A valid encoded numeral, n, is detected by the photodetectorarray 38 only during transillumination of the encoder disc 34 by NIRlight beam 36. A “data valid” command is generated by logical OR of eachof the bits of the binary encoded numeral, n, or by using a singleseparate photodetector with an additional optical window at eachdiscrete static position of the valve mechanism axis 26. The “datavalid” signal provides a ‘load’ command 40 to a latch 42 which storesthe encoded binary numeral, n.

The encoded binary numeral, n, is used as the divisor for a divide-by-ncounter 44. A crystal oscillator 46 provides a stable referencefrequency 48, f_(in), which is divided by the divisor ratio, n.Therefore, the output frequency 50, f_(out), is uniquely dependent uponthe valve mechanism axis 26 position, and hence the pressure to valve18. The near infrared emitter 52 is driven at the output frequency 50.The infrared beam 54 is passed through a beam-splitter mirror 56 suchthat a portion of the infrared light beam 36 is used to transilluminatethe optical encoder disc 34. The remainder of beam 54 travels throughthe skin 20 to become the transcutaneous NIR beam 58. The transcutaneousbeam 58 is detected by a photodetector 82 within sensor head andprocessing electronics 62 after passing through a narrow bandpass filter64. The narrow bandpass filter 64 excludes ambient light at wavelengthsother than that expected from the NIR emitter 52. The frequency of thephotodetector 82 output is measured at 63 and is used to index a look-uptable 60 which correlates the modulation frequency 50 with the actualvalve pressure setting which is then displayed at 68.

FIG. 3 illustrates representative electronic circuitry for the implant.A crystal oscillator composed of crystal X1, inverters U1a-c, capacitorsC1, C2 and feedback resistor R9, provides a reference frequency toprogrammable divider U2. The reference frequency is divided by n and theoutput used to gate the VCSEL, D3, via transistor Q7. Transistor Q8 andresistor R8 act to regulate the maximum current through D3.

Light from the VCSEL is detected by an array of photodetectors Q1-Q6.During VCSEL illumination, the disc 34 (FIG. 2) allows selectiveillumination of phototransistors Q2-Q6, thus providing a binaryrepresentation of the frequency divisor. The light path from the VCSELto Q1 is never obstructed, despite the position of disc 34 so that Q1conducts each time the VCSEL illuminates. The output of Q1 is fed toinverter U1d which, in turn, asserts a positive-going ‘load’ signal toU2 as the VCSEL illuminates. Upon assertion of the ‘load’ signal, thefrequency divider divisor data is latched on U2 inputs D0-D4. A smallcapacitance, on the order of several picofarads, may be placed on thebase of transistor Q1 to allow Q2-Q6 to stabilize prior to asserting the‘load’ signal. A period of 2^(N) clock pulses may be necessary for theoutput frequency to stabilize.

FIG. 4 depicts a block diagram of the external circuitry which: 1)provides power to the implant; 2) detects the NIR emission from theimplant; and, 3) converts the frequency data from the implant to agraphical representation of valve position.

Sensor head 70 is placed over the implant to deliver power and detectthe optical output of the implant. A power oscillator 72 delivers asinusoidal oscillating current with a nominal frequency of 200 kHz to apower amplifier 74 which buffers the current to an isolation transformer76. The isolation transformer 76 provides adequate galvanic isolationfor a patient-connected device. The output from the isolationtransformer is fed to the sensor head coil 78 which acts as the primarywinding of a transformer to electromagnetically couple energy to theimplant's secondary coil L1 (FIG. 3).

An optical bandpass filter 64 with center frequency equal to theemission frequency of the VCSEL, excludes ambient light from thephotodetector 82. Light from the implant VCSEL is transmitted throughbandpass filter 64 and converted to an electrical current byphotodetector 82. This current is roughly a square wave with the samefundamental frequency as the VCSEL pulses. This signal is amplified bypre-amp 84 and automatic gain amplifier 86, then converted to a digitalsignal by Schmitt trigger 88. A serial data stream 90, consisting ofsquarewave pulses, is fed to microprocessor 92 which measures thefrequency of the aforementioned pulses. The frequency data is then usedto index a look-up table 60 (FIG. 2) through software programming; theresult of which is a numerical indication of the valve pressure setting.The result is displayed for the user upon a digital or other graphicaldisplay 68.

A bi-colored Light Emitting Diode, or LED, is also included in thesensor head 70 to aid positioning of the sensor head over the implant.In the default state, the red LED 96 is illuminated to indicate that thesensor head is not over the implant. When the sensor head is properlyaligned over the implant, the implant begins to receive power throughthe inductive coupling between coil 78 of the sensor head and Li of theimplant. Once power is applied to the implant, the VCSEL begins toilluminate in synchrony with the programmable divider (U2) output. Whenthe External device begins to detect the VCSEL, e.g. oscillationspresent on the ‘serial data’ output of Schmitt Trigger 88, themicroprocessor 92 turns off the red LED 96 and illuminates the green LED94.

While the present invention has been described in terms of specificembodiments thereof, it will be understood in view of the presentdisclosure, that numerous variations upon the invention are now enabledto those skilled in the art, which variations yet reside within thescope of the present teaching. Accordingly, the invention is to bebroadly construed, and limited only by the scope and spirit of theclaims now appended hereto.

1. In a programmable valve system of the type which is implanted in amedical patient and used to divert cerebrospinal fluid (CSF) from anintraventricular space of the patient to a terminus such as the patientperitoneal cavity; said system including means for establishing a flowpath for said CSF to said terminus, which flow path includes a normallyclosed valve and means for adjusting the opening pressure of said valvein order to regulate the quantity of CSF diverted; the improvementenabling an observer to be apprised of the actual opening pressuresetting of the said valve, comprising: (a) means implantable at saidpatient and responsive to said actual opening pressure setting forgenerating an NIR telemetry signal indicative of said actual setting fortranscutaneous transmission through the skin of said patient to anexternal point; and (b) means positionable externally of said patientfor receiving said telemetry signal at said external point and forproducing therefrom observer intelligible data indicating the saidactual opening pressure setting of said valve.
 2. A system in accordancewith claim 1, wherein said means implantable at said patient includes avertical cavity surface emitting laser (VCSEL) for generating NIR lightfor said telemetry signal.
 3. A system in accordance with claim 1,wherein said opening pressure of said valve is determined by therotational position of a valve mechanism axis; and wherein said meansresponsive to said actual value of said pressure setting comprises anoptical encoder disc which is rotatable with said axis; and means forutilizing the rotational position of said disc to control the said NIRtelemetry signal.
 4. A system in accordance with claim 3, wherein eachspecific static rotational angle which may be assumed by said valvemechanism axis has a corresponding unique encoded binary numeral n; andwherein said means (a) includes means for transilluminating said discwith said NIR light, and a photodetector positioned for detecting NIRlight passing through NIR-pervious radically oriented regions positionedperiodically about said disc; means for determining from the lightpassed through the illuminated said region the angular position of saiddisc and thereby of said axis; and means for modulating said NIRtelemetry signal to reflect the thereby determined rotational positionof said axis.
 5. A system in accordance with claim 4, wherein said NIRtelemetry signal is modulated so that the output frequency of thetelemetry signals has a frequency depended on the rotational position ofsaid valve mechanism axis.
 6. A system in accordance with claim 5, wherethe telemetry signal detected at said sensor head is used to index alook-up table which correlates the modulation frequency with the actualpressure at said valve.
 7. A system in accordance with claim 6, whereinthe resulting said actual valve pressure is displayed for use by saidoperator.
 8. A system in accordance with claim 1, including means atsaid sensor head to verify positioning of the sensor head over and incoupling relation with said implant means (a).
 9. A system in accordancewith claim 8, wherein said means for verifying positioning of saidsensor head is a visually discernable LED.
 10. A system in accordancewith claim 1, wherein power for said implant is provided from a pointexternal to said patient by inductive coupling with a coil at saidsensor head.
 11. A system for retrieving the biometric pressure datafrom a programmable valve implanted in an organism comprising: anintracorporeal device sealed within the organism; an extracorporealdevice outside the organism; a freespace optical data channelestablished between the intracorporeal device and the extracorporealdevice for communication of the biometric pressure data; a freespaceelectromagnetic power transmission channel established from theextracorporeal device to the intracorporeal device for transmission ofpower; and a freespace mechanical power transmission channel establishedfrom the extracorporeal device to the intracorporeal device formanipulation of a position of the intracorporeal device.
 12. The systemof claim 11 wherein the freespace optical data channel is bidirectional.13. The system of claim 11 wherein the freespace optical data channel isin a wavelength range between 800 nm and 1000 nm.
 14. The system ofclaim 11 wherein the intracorporeal device is powered only upon receiptof a transmission of power from the electromagnetic power transmissionchannel.
 15. The system of claim 14 wherein a light emitting diode onthe extracorporeal device illuminates when the intracorporeal devicereceives power.
 16. The system of claim 11 wherein the extracorporealdevice includes a processor for operating on the transmitted nearinfrared form.
 17. The system of claim 16 further comprising a memorymeans, in communication with the processor, for storage of a data setrelated to the angular position of the valve.
 18. The system of claim 17wherein the processor is further programmed to conduct signal processingon the data set.
 19. The system of claim 11 wherein the extracorporealdevice further comprises a coupling module, an analysis module and anexternal mechanical programmer.
 20. The system of claim 19 wherein thecoupling module further comprises: an optical receiver coupled to thefreespace optical data channel and; a power transmitter coupled to theelectromagnetic power transmission channel.
 21. The system of claim 19wherein the external mechanical programmer further comprises: a drivermagnet coupled to the freespace mechanical power transmission channel.22. The system of claim 19 wherein the analysis module furthercomprises: an optical receiver coupled to the freespace optical datachannel; a decoder coupled to the optical receiver; and a processorconnected to the decoder programmed to interpret the biometric data. 23.The system of claim 19 wherein the power transmitter further includes: apower signal conditioner; and a transformer connected to the powersignal conditioner and to the power transmitter.
 24. The system of claim11 wherein the intracorporeal device further includes an encoding systemfor generating a signal related to an angular position of the valvedata.
 25. The system of claim 24 wherein the encoding system furthercomprises: an encoder disk; an optical source adjacent to the encoderdisk; an optical receiver in communication with the optical source forgenerating an encoded signal related to the angular position of theencoder disk; and an optical transmitter coupled to the freespaceoptical data channel adapted to transmit the encoded signal.
 26. Thesystem of claim 24 wherein the encoder disk further comprises: anoptically opaque disk having an encoder pattern and a reference pattern;a light source adjacent to the optically opaque disk and adapted totransmit light through the encoder pattern and the reference pattern; afirst reference array adjacent the encoder pattern adapted to receivelight through the encoder pattern and generate an angular positionsignal indicative of the angular position of the encoder disk; a secondreference array adjacent the reference pattern adapted to receive lightthrough the reference pattern and generate a data valid signalindicative of the validity of the angular position signal.
 27. A methodof moving an implanted device in an organism comprising the steps of:activating the implanted device through an inductively coupled powersource; electromagnetically creating an altered position of the device;and deriving an optical data signal from the altered position; andtransmitting it out of the organism.
 28. The method of claim 27 whereinthe step of activating comprises the further steps of: generatingelectromagnetic power signal by an extracorporeal device; and receivingof the electromagnetic power signal by the implanted device.
 29. Themethod of claim 27 wherein the step of collecting comprises the furthersteps of: generating a data signal in response to the position of avalve coupled to the implanted device; and transforming the data signalinto the near infrared signal.
 30. The method of claim 27 wherein thestep of electromagnetically creating further comprises: rotating adriver magnet above the implanted device.